This invention relates to a system for transmitting data between a rotating body and a stationary device. More particularly, this invention relates to an RF system that is used to transmit data between a drill casing and a stationary receiver. Still more particularly, this invention relates to n phased patch antennas affixed around an outer surface of the rotating body and a transmitter that sequentially applies n RF signals, where n is an integer greater than 1, that are phased 360xc2x0/n apart to the antennas.
It is a problem in the well drilling arts to receive hole data from the drill and casing as the drill is being operated. One must understand drilling operations to understand the problems of collecting the data. In order to drill a well, a platform is constructed over a desired location. The platform has a motor which turns a casing that is connected to a drill bit. As the drill bit is turned, the casing is forced downward. The casing is hollow and liquid is pumped into the casing to cool the drill bit and to remove excess material from the hole. Once a section of casing has been extended into the hole, an additional section of casing is affixed to a top end of a prior section of casing to lengthen of the casing.
Sensors are typically attached to the casing and to the drill bit to measure hole and equipment characteristics. It is a problem to retrieve the data from the sensors. Data must be received quickly during the drilling process to detect possible problems so that drilling operations can be halted or altered to eliminate the problem. Therefore, it is desireable to receive the data as soon as it is collected.
A first problem that is particular to retrieving data from a rotating drill casing and applies generally to rotating objects is the rotation of the casing. The rotation of the casing makes it impossible to use a physical connection such as a data line connected to the casing to retrieve data. The data lines would wrap around the casing as the casing rotates.
In order to solve this problem, Radio Frequency (RF) signals can be used to transmit data between a rotating body, such as the well casing, and a stationary object. However, some particular problems arise from using RF signals. One problem is affixing antenna to the rotating object. The antennas must rotate with the object. The rotation of the antenna causes the antennas to rotate out of range of one stationary antenna. This can cause data to be missed as RF signals from the rotating antenna are not received by the stationary antenna. Furthermore, the stationary antenna must be proximate the rotating object to maximize the range that the antenna can receive signals during a rotation. This is a problem on a drilling platform because space on the platform is limited and it is likely that the heavy equipment on the platform could damage a stationary antenna mounted on the platform during drilling operations.
There is a need in the art for an RF system that can reliably transmit data between a rotating body and a stationary RF system. Furthermore, there is a particular need in the drilling art for an RF system that can increase the distance between RF system on a rotating drill casing and a receive antenna.
The above and other problems are solved and an advance in the art is made by the provision of a rotating RF system. The rotating RF system reduces the amount of data that is lost as an antenna on a rotating body rotates out of range of a stationary antenna. The rotating RF system also allows the stationary antenna to be placed further away from the rotating body. This allows the stationary antenna to be place off a drilling platform in a preferred exemplary embodiment.
The rotating RF system has n patch antennas affixed around the outer surface of a rotating body, such as a drill casing. In a preferred embodiment, each of the n patch antennas is horizontally phased which allows each antenna to broadcast RF signals outward from the rotating body in a direction substantially perpendicular to the outer surface of the rotating body. By directing the broadcast RF signals in a focused direction, the stationary antenna may be moved farther away from the routing body, since the stationary antenna must remain in communication with one of the n patch antennas for only a limited amount of the rotation.
RF signals transmitted by the patch antennas are generated in the following manner to reduce the amount of data that is lost. A transmitter in the rotating body generates an RF signal with encoded data. The RF signal is then applied to circuitry that splits the RF signal into n identical RF signals. The n RF signals are then phase shifted to create n RF signals that each are phased three hundred and sixty divided by n degrees apart. The first RF signal is phase shifted by zero degrees and the nth RF signal is phase shifted by 360xc2x0 minus 380xc2x0/n degrees.
The n RF signals are then sequentially applied to the n patch antennas. The following is an example of sequentially applying the n RF signals to the n patch antennas. The first RF signal having a phase shift of zero degrees is applied to a first antenna. A second RF signal having a phase shift of three hundred and sixty divided by n is applied to a second patch antenna which affixed to the outer surface of the rotating body in a position that allows the second antenna to come into range of the stationary antenna as the first antenna rotates out of range of the stationary antenna. The remaining nxe2x88x922 signals are similarly applied to the remaining nxe2x88x922 patch antennas.
As the rotating body rotates, the one patch antenna is broadcasting towards the stationary antenna. As the broadcasting antenna moves out of range, a second antenna rotates into range and begins broadcasting to the stationary antenna. The RF signals from the second antenna are phased shift 360xc2x0/n from the RF signals from the first antenna. This assures that a redundant signal is provided as the transmitting patch antennas change this assures that data is not lost during the change.
In a preferred embodiment of the present invention, the rotating RF system also has at least one receive antenna connected to the outer surface of the rotating body to allow a stationery transmit antenna to transmit RF signals to the rotating body.